1. Field of the Invention
The present invention relates to an X-ray computer tomography apparatus.
2. Description of the Related Art
In a present X-ray computer tomography apparatus, continuous X-rays are mainly used. While X-rays are continuously irradiated on a subject, data collection is repeated at a constant cycle. A data collection cycle roughly consists of a charge storage period, a signal charge read-out period, and a charge reset period. Theoretically, only X-rays irradiated within the charge storage period are reflected on data. Therefore, it is effective for a reduction in exposure to irradiate a pulse-like X-ray on a subject in synchronization with the charge storage period rather than continuously irradiating X-rays on the subject. However, under the present situation in which an ultra-fast scan with a scan time of 0.5 seconds or less is mainly used, the irradiation of a pulse-like X-ray is not adopted because a load on a high-voltage generation apparatus is large. In addition, there is a disadvantage that, when it is attempted to create an X-ray of a short pulse, a surface exposure dose increases because an X-ray with low energy is generated at a rising edge of the pulse.
Therefore, as described in Japanese Patent Nos. 2704084, 2768932, and 3394038 and JP-A-10-295681, under the present situation, an exposure dose is adjusted according to tube current control.